Apparatus and method for filtering data influenced by a downhole pump

ABSTRACT

Disclosed is a method for transmitting data from a tool disposed in a borehole penetrating the earth to a receiver. The method includes disposing the tool in a borehole and receiving a series of measurements using a processor disposed at the tool. A telemetry system transmits a latest received measurement that meets acceptance criteria to the receiver after completion of transmission of a previously transmitted measurement.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of an earlier filing date from U.S.Provisional Application Ser. No. 61/467,262 filed Mar. 24, 2011, theentire disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The invention disclosed herein relates to filtering data obtained from adownhole environment and, in particular, to data related to using adownhole pump.

2. Description of the Related Art

Drilling apparatus used for geophysical exploration often includes oneor more sensors for performing measurements on ambient subsurfacematerials. In performing measurements referred to asmeasure-while-drilling or MWD, the sensors are disposed in a bottomholeassembly located in a drill string in the vicinity of a drill bit. Themeasurements can be performed while drilling a borehole through thesubsurface materials or during a temporary halt in drilling.

Data related to the measurements is typically transmitted to the surfaceof the earth using mud-pulse telemetry. Mud-pulse telemetry is usuallyvery slow (a few bits per second) taking several seconds to minutes totransmit a whole data package. Because of the low data transmissionrate, problems can arise when all the acquired data cannot betransmitted. Usually the latest acquired data available is used fortransmission to the surface. However, not all of the latest acquireddata is useful and transmission of such data wastes time and bandwidthand can prevent more useful data from being transmitted.

One type of sensor used to MWD is a formation tester tool. The formationtester tool is configured to draw formation fluid from a wall of theborehole and to perform one or more tests on the formation fluid sample.A positive displacement pump such as a dual action pump using a pistonis typically used to draw the formation fluid sample. The sample isdrawn by the piston reducing pressure within a chamber causing theformation fluid, which is at a higher pressure, to flow into thechamber. However, when the piston reverses its stroke, inlet flow stopsand the sample chamber pressure rises towards the formation pressure.Sample pressure or a parameter related to sample pressure is generallyone type of data required to properly evaluate the sample. Sometimes thepressure is transmitted while the piston is moving and sometimes thepressure is transmitted while the piston is reversing (i.e., stopped).Transmitting a value measured during pump reversing is a waste of timeand bandwidth because the value it is transmitted at non-predictableintervals. Hence, it would be well received in the drilling industry ifthe transmission of data from a MWD tool could be improved.

BRIEF SUMMARY

Disclosed is a method for transmitting data from a tool disposed in aborehole penetrating the earth to a receiver. The method includesdisposing the tool in a borehole and receiving a series of measurementsusing a processor disposed at the tool. A telemetry system transmits alatest received measurement that meets acceptance criteria to thereceiver after completion of transmission of a previously transmittedmeasurement.

Also disclosed is an apparatus for transmitting data from a toolconfigured to be disposed in a borehole penetrating the earth to areceiver. The apparatus includes: a telemetry system disposed at thetool; and a processor disposed at the tool and configured to receive aseries of measurements and to identify those measurements that arelatest received and meet an acceptance criterion for transmission by thetelemetry system to the receiver after completion of transmission of apreviously transmitted measurement.

Further disclosed is a non-transitory computer-readable medium havingcomputer-executable instructions for transmitting data from a tooldisposed in a borehole penetrating the earth to a receiver byimplementing a method that includes: receiving a series of measurementsfrom a sensor disposed in a borehole; and transmitting a latest receivedmeasurement that meets an acceptance criterion to the receiver aftercompletion of transmission of a previously transmitted measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 illustrates an exemplary embodiment of a downhole tool disposedin a borehole penetrating the earth;

FIG. 2 illustrates an exemplary embodiment of a dual-action sample pump;

FIG. 3 depicts aspects of sample chamber pressure in the sample pump;

FIGS. 4A and 4B, collectively referred to as FIG. 4, depict furtheraspects of sample chamber pressure in the sample pump;

FIGS. 5A and 5B, collectively referred to as FIG. 5, depict aspects ofsensor output influenced by pump pressure variation; and

FIG. 6 presents one example of a method for transmitting data from adownhole tool to a receiver.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method presented herein by way of exemplification and notlimitation with reference to the Figures.

FIG. 1 illustrates an exemplary embodiment of a downhole tool 10disposed in a borehole 2 penetrating the earth 3, which includes anearth formation 4. The downhole tool 10 is conveyed through the borehole2 by a carrier 5. In the embodiment of FIG. 1, the carrier 5 is a drillstring 6 for measurement-while-drilling (MWD) operations. In anotherembodiment, the carrier 5 can be a wireline for wireline operations. Atelemetry system 7 is provided in order to transmit data from thedownhole tool 10 to a receiver such as a computer processing system 13disposed at the surface of the earth 3. In one embodiment, the telemetrysystem 7 is a mud-pulse telemetry system 8. In order to operate thedownhole tool 10 and/or provide a communications interface with thetelemetry system 7, the downhole tool 10 includes downhole electronics11.

Still referring to FIG. 1, the downhole tool 10 includes a formationfluid tester 12 configured to perform one or more measurements on fluidextracted from the formation 4. The formation fluid tester includes aprobe 14 configured to extend from the downhole tool 10 and seal with awall of the borehole 2. A pump 15 coupled to the probe 14 is configuredto lower the pressure internal to the probe 14 in order to draw a sampleof formation fluid from the formation 4 and discharge the sample into asample chamber 16 for analysis. Various sensors 17 are configured toperform various types of measurements on the sample. Non-limitingexamples of the measurements include pressure, temperature, density,viscosity, compressibility, radiation, and spectroscopy.

Still referring to FIG. 1, the downhole electronics 11 includes a filter18 configured to process data/measurements from the various sensors 17.The processing can include a filtering function and/or an associatingfunction where each measurement received is associated with some otherdata such as a measurement of some aspect of the pump 15. The downholeelectronics 11 also includes memory 19 configured to store measurementsfrom the sensor 17 as the measurements are received. The memory 19provides for storing measurements that cannot be immediately transmittedto the computer processing system 13 because of limited bandwidth of thetelemetry system 7.

Reference may now be to FIG. 2 illustrating an exemplary embodiment ofthe pump 15. In the embodiment of FIG. 2, the pump 15 is a dual-actionpump (i.e., pumping fluid on both strokes of a piston). A piston in pump15 is used to displace fluid to cause the pumping. While pumping, valves21 and 22 act as inlet valves and valves 23 and 24 act as outlet valves.Valves 21-24 can be check-valves or externally driven valves. Coupled tothe pump 15 is a pump sensor 20. The pump sensor 20 is configured tomeasure one or more aspects of the pump 15. As non-limiting examples,the pump sensor 20 can measure inlet pressure, outlet pressure, pistonposition, pump flow rate, and/or volume pumped.

One property of a piston based dual-action pump is that it cannotgenerate a continuous flow. When the piston has reached an end stop, thedirection must be reversed and optionally some valves must be actuated.Pump reversal takes some amount of time during which no flow isgenerated. In a fluid sampling application, the stopping of flow leadsto increasing pressure on the inlet side. The pressure rises towardsformation pressure (and is referred to as build-up). FIG. 3 presents apressure curve of a dual-action pump for one of the inlet sides of thepump.

As noted in FIG. 3, pressure is relatively constant when the piston ismoving. Hence, in one embodiment, transmission of the latest dataacquired is the transmission of the latest data obtained while thepiston is moving. If a telemetry data request is received by the tool10, the returned data is either (case 1) the latest value if the pistonis currently moving or (case 2) an older value (stored in memory) thatwas acquired while the piston was moving if the piston is currentlyreversing. Directly after pump reversal, the pressure needs some time tostabilize again. A further improvement to the above method is to includesome time for piston movement after piston reversal such as in case 2.This additional time can be defined by a specific or set time, a volumepumped, a flow rate, or data stability of some sensor data. If thepiston position is known, there is no need to detect if the piston hasstopped. Case 2 can be entered when pump piston reversal is imminent.Each of the required conditions for data to be transmitted to thereceiver may be referred to as an acceptance criterion.

The techniques for determining which data to transmit can be extendedfrom pump inlet pressure measurement to other data. Downhole fluidsampling tools may contain fluid sensors for fluid contaminationestimation or fluid identification or characterization. The output ofthese sensors can be pressure dependent. If a pressure variation iscaused by the pump and influences the sensor data, an algorithm can beused to determine and transmit consistent data (i.e., data taken underapproximately the same conditions). This way, a tool operator can betterassess if variation in sensor data is caused by a change in fluidproperties. It reduces the probability for misinterpretation because thetransmitted data shows less variation and is known to be more consistentand, thus, yield more accurate data.

In general, the operator must make sure that the inlet pump pressuredoes not get below a threshold pressure (e.g., bubble point) at whichthe fluid properties change irreversibly. Hence, the tool operator isusually interested in the lower pressures. For this reason, oneadditional type of data to transmit is the lowest pump inlet pressure,which has occurred in a certain timeframe. This value helps the tooloperator to decide if the pump speed must be adjusted to stay above thebubble point. The timeframe can be defined by a time interval, volume,or telemetry update rate as non-limiting examples. The idea of sendingadditional data to help interpret the primary data sent can be extendedto other sensor data that is influenced by pressure or flow ratevariation and where minimum, maximum, or other statistical values areimportant for the tool operator to know when the data transmission rateis too low to determine these values after transmission of raw data.

If pump speed is low, the time to fill a pump chamber can be long. Fluidentering the pump chamber may contain immiscible components orcomponents featuring high difference in density. A long staying time inthe pump chamber can lead to segregation of the fluid components. Whenthe segregated fluid is pushed out of the chamber, the components mayleave the chamber successively, influencing the fluid sensorssuccessively as well. Usually, this leads to random noise in thetelemetry data. In order to compensate for measurements of the differentcomponents, the measured data can be separated into data acquired at thebeginning of a pump stroke from the data acquired at the end of the pumpstroke. Thus, consistent data for the individual fluid components istransmitted.

Extraction and transmission of data acquired while the pump is reversingcan give information about mobility (i.e., higher mobility leads tohigher pressure or faster pressure stabilization at formation pressureduring stopping of flow). Pressure rising above formation pressureduring stopping of flow is an indicator for loss of seal with theformation. This information is very important because the loss of sealusually cannot be remedied except by aborting tool operation, releasingthe seal element, moving the tool to a different location and trying toachieve a seal at the new location. Hence, for these reasons it may bedesirable to transmit data obtained during reversal of the pump piston.

Some sensors are influenced by the pressure or flow rate variationscaused by the pump. Some measurements take a long time to deliver aresult, or long time response filters are involved in post-processing ofthe measurements. If this timeframe overlaps with pump piston reversal,the sensor data quality will suffer.

In a first example, a sensor is influenced by the pressure or flow ratevariations caused by the pump. Its data is acquired at a high rate andfiltered by a filter with a filter response time of several seconds. Thepressure change during pump piston reversal generates biased acquireddata and the filtered data will still be biased for some time after thepump piston reversal has been executed because of the filter delay.

In a second example, a sensor is influenced by pump pressure variation.A measurement takes several seconds. The sensor might feature avariation of a resonance frequency as response to a parameter ofinterest. To measure the parameter of interest, the resonance has to bedetermined by applying a frequency sweep. This can take several seconds.If a pressure variation occurs during the sweep, the acquired spectrumis distorted (maybe showing several resonance peeks or none at all) andthe result can be of limited value or useless.

In order to accommodate sensors with long acquisition time windows andfilters with long response times, sensor data acquisition can be pausedduring pump piston reversal. Sensor data acquisition is then resumedafter pump piston reversal when the pump inlet pressure is stable again.If the pump piston position is known, the data acquisition can alreadybe paused when the pump piston reversal is imminent. Pausing can include(1) stopping data acquisition completely and stopping the associatedfiltering as well (such as when using digital filters), (2) feeding thelast good value (i.e., stable constant value) into the filter, (3)stopping a measurement sequence and resuming it later (for example,stopping the frequency sweep at the current frequency and resuming thefrequency sweep at that frequency later), and (4) discarding alreadyacquired data of a measurement sequence and restarting the sequencelater.

It can be appreciated that the methods described above for dataacquisition and transmission can be used for data post-processing anddata display. Separating data acquired during flow and no-flow pumpphases leads to less noisy and more clear and accurate data curves byseparating the relevant information. FIG. 4A shows one example oforiginal (i.e., unfiltered) data for pump pressure versus time whileFIG. 4B shows that data after filtering (i.e., cleaned-up postprocessing data). FIG. 5A shows another example of original unfiltereddata, in this case sound speed versus time, while FIG. 5B shows thatdata after filtering.

Combination of data acquired during flow and no-flow phases of the pumpcan be used to estimate additional fluid properties. If the pressure (orflow rate) change is known and the response of an additional sensor topressure (or flow rate) change is also known, then properties such asfluid compressibility or viscosity related properties or thermalproperties can be estimated. For example, fluid pressure during flow andduring no-flow phases of the pump can be acquired. Additionally, fluidsound speed as well as refractive index during flow and no flow phasescan also be acquired, while the density is determined only during flowcondition. The fluid's compressibility and density determine the soundspeed of a fluid according to equation (1) where κ is compressibility.

$\begin{matrix}{c^{2} = \frac{1}{\kappa \; \rho}} & (1)\end{matrix}$

The fluid's density, sound speed and refractive index ρ₁, c₁ and n₁,respectively, during flow phase are given as are the fluid's sound speedand refractive index c₂ and n₂ during no-flow phase. Because thepolarizability of the fluid is not changed during the short flow stop,the density ρ₂ can be calculated following Clausius-Mosotti equation, asexplained in patent U.S. Pat. No. 7,016,026 B2 using equation (2).

$\begin{matrix}{\rho_{2} = {\rho_{1}{\frac{n_{2}^{2} - 1}{n_{2}^{2} + 2} \cdot \frac{n_{1}^{2} + 2}{n_{1}^{2} - 1}}}} & (2)\end{matrix}$

The compressibility for both flow conditions can therefore be calculatedusing equations (3) and (4).

$\begin{matrix}{\kappa_{flow} = \frac{1}{c_{1}^{2}\rho_{1}}} & (3) \\{\kappa_{{no}\text{-}{flow}} = {\frac{1}{c_{2}^{2}\rho_{1}} \cdot \frac{n_{2}^{2} + 2}{n_{2}^{2} - 1} \cdot \frac{n_{1}^{2} - 1}{n_{1}^{2} + 2}}} & (4)\end{matrix}$

Additionally, significant changes in fluid compressibility between theflow and no-flow condition can be used as an indicator for bubble pointpressure undershoot.

FIG. 6 presents one example of a method 60 for transmitting data from atool disposed in a borehole penetrating the earth to a receiver. Themethod 60 calls for (step 61) disposing the tool in a borehole using acarrier. Further, the method 60 calls for (step 62) receiving a seriesof measurements using a processor disposed at the tool. Further, themethod 60 calls for (step 63) transmitting a latest received measurementthat meets an acceptance criterion to the receiver after completion oftransmission of a previously transmitted measurement using a telemetrysystem.

In support of the teachings herein, various analysis components may beused, including a digital and/or an analog system. For example, thedownhole electronics 11, the computer processing system 13, or thefilter 18 may include the digital and/or analog system. The system mayhave components such as a processor, storage media, memory, input,output, communications link (wired, wireless, pulsed mud, optical orother), user interfaces, software programs, signal processors (digitalor analog) and other such components (such as resistors, capacitors,inductors and others) to provide for operation and analyses of theapparatus and methods disclosed herein in any of several mannerswell-appreciated in the art. It is considered that these teachings maybe, but need not be, implemented in conjunction with a set of computerexecutable instructions stored on a computer readable medium, includingmemory (ROMs, RAMs), optical (CD-ROMs), or magnetic (disks, harddrives), or any other type that when executed causes a computer toimplement the method of the present invention. These instructions mayprovide for equipment operation, control, data collection and analysisand other functions deemed relevant by a system designer, owner, user orother such personnel, in addition to the functions described in thisdisclosure.

Further, various other components may be included and called upon forproviding for aspects of the teachings herein. For example, a powersupply (e.g., at least one of a generator, a remote supply and abattery), cooling component, heating component, magnet, electromagnet,sensor, electrode, transmitter, receiver, transceiver, antenna,controller, optical unit, electrical unit or electromechanical unit maybe included in support of the various aspects discussed herein or insupport of other functions beyond this disclosure.

The term “carrier” as used herein means any device, device component,combination of devices, media and/or member that may be used to convey,house, support or otherwise facilitate the use of another device, devicecomponent, combination of devices, media and/or member. Other exemplarynon-limiting carriers include drill strings of the coiled tube type, ofthe jointed pipe type and any combination or portion thereof. Othercarrier examples include casing pipes, wirelines, wireline sondes,slickline sondes, drop shots, bottom-hole-assemblies, drill stringinserts, modules, internal housings and substrate portions thereof.

Elements of the embodiments have been introduced with either thearticles “a” or “an.” The articles are intended to mean that there areone or more of the elements. The terms “including” and “having” areintended to be inclusive such that there may be additional elementsother than the elements listed. The conjunction “or” when used with alist of at least two terms is intended to mean any term or combinationof terms. The terms “first” and “second” are used to distinguishelements and are not used to denote a particular order.

It will be recognized that the various components or technologies mayprovide certain necessary or beneficial functionality or features.Accordingly, these functions and features as may be needed in support ofthe appended claims and variations thereof, are recognized as beinginherently included as a part of the teachings herein and a part of theinvention disclosed.

While the invention has been described with reference to exemplaryembodiments, it will be understood that various changes may be made andequivalents may be substituted for elements thereof without departingfrom the scope of the invention. In addition, many modifications will beappreciated to adapt a particular instrument, situation or material tothe teachings of the invention without departing from the essentialscope thereof. Therefore, it is intended that the invention not belimited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A method for transmitting data from a tool disposed in a boreholepenetrating the earth to a receiver, the method comprising: disposingthe tool in a borehole using a carrier; receiving a series ofmeasurements using a processor disposed at the tool; and transmitting alatest received measurement that meets an acceptance criterion to thereceiver after completion of transmission of a previously transmittedmeasurement using a telemetry system.
 2. The method according to claim1, further comprising storing each measurement in the series ofmeasurements in memory disposed in the tool.
 3. The method according toclaim 1, further comprising associating each measurement with anacceptance criterion measurement performed by a first sensor.
 4. Themethod according to claim 3, further comprising comparing the acceptancecriterion measurement to the acceptance criterion in order to determineif the associated measurement should be transmitted to the receiver. 5.The method according to claim 4, further comprising transmitting theseries of measurements from a second sensor disposed at the tool.
 6. Themethod according to claim 5, wherein the second sensor is configured tosense a downhole property of interest.
 7. The method according to claim6, wherein in the downhole property of interest is a formation fluidproperty.
 8. The method according to claim 7, further comprisingextracting the formation fluid from an earth formation using a pump. 9.The method according to claim 8, further comprising performing theacceptance criterion measurement on the pump using the first sensor. 10.The method according to claim 9, wherein the acceptance criterionmeasurement comprises a selection from a group consisting of a pumppiston stroke position, a time after a pump piston travel reversal, apump flow rate, a volume pumped, or some combination thereof.
 11. Themethod according to claim 10, wherein the pump piston stroke positioncomprises a position approximately half way between two stroke reversingpositions.
 12. The method according to claim 10, wherein the pump flowrate is approximately constant for a certain amount of time.
 13. Themethod according to claim 10, further comprising separating firstmeasurements associated with a first value of a selected acceptancecriterion measurement from second measurements associated with a secondvalue of the selected acceptance criterion measurement.
 14. The methodaccording to claim 13, wherein the first value is related to a stableflow rate of fluid through the pump and the second value is related to aflow rate of fluid through the pump that is less than the stable flowrate.
 15. The method according to claim 14, further comprisingdetermining the compressibility of the pumped fluid using the firstmeasurements and the second measurements.
 16. The method according toclaim 8, wherein the pump comprises a piston configured to pump a fluidby displacement, the method further comprising separating firstmeasurements performed when the piston is approximately reversingdirection from second measurements performed when the piston is movingand pump inlet pressure is stabilized.
 17. The method according to claim16, further comprising associating a first component of the pumped fluidwith the first measurements and a second component of the pumped fluidwith the second measurements.
 18. An apparatus for transmitting datafrom a tool configured to be disposed in a borehole penetrating theearth to a receiver, the apparatus comprising: a telemetry systemdisposed at the tool; and a processor disposed at the tool andconfigured to receive a series of measurements and to identify thosemeasurements that are latest received and meet an acceptance criterionfor transmission by the telemetry system to the receiver aftercompletion of transmission of a previously transmitted measurement. 19.The apparatus according to claim 18, wherein the processor is furtherconfigured to store each measurement in the series of measurements inmemory disposed at the tool.
 20. The apparatus according to claim 18,further comprising a first sensor configured to provide to the processoran acceptance criteria measurement associated with each measurement inthe series of measurements.
 21. The apparatus according to claim 20,further comprising a second sensor configured to provide the series ofmeasurements, wherein the measurements are of a downhole property ofinterest.
 22. The apparatus according to claim 21, further comprising apump configured to extract a formation fluid from an earth formation,wherein the second sensor is further configured to perform a measurementof a property of the extracted formation fluid.
 23. The apparatusaccording to claim 22, wherein the first sensor is coupled to the pumpand configured to measure a parameter of the pump.
 24. The apparatusaccording to claim 18, wherein the telemetry system is a mud-pulsetelemetry system.
 25. The apparatus according to claim 18, wherein thetool is disposed at a carrier configured to be conveyed through theborehole.
 26. The apparatus according to claim 25, wherein the carriercomprises at least one of a drill string, coiled tubing, a wireline, anda slickline.
 27. A non-transitory computer-readable medium comprisingcomputer-executable instructions for transmitting data from a tooldisposed in a borehole penetrating the earth to a receiver byimplementing a method comprising: receiving a series of measurementsfrom a sensor disposed in a borehole; and transmitting a latest receivedmeasurement that meets an acceptance criterion to the receiver aftercompletion of transmission of a previously transmitted measurement.